1. Field of the Invention
The present invention relates to a method of heating films for thermoforming. More specifically, the invention relates to a method for heating a painted film with a colored layer and a clear coating that are easily damaged by exposure to excessive heat.
2. Description of the Related Arts
It is known to manufacture molded articles by using pre-molded film laminates. A flexible film having a painted surface and a backing surface is thermoformed into the shape of the final article and placed within a molding press. The thermoforming operation requires that the film be heated to make it pliable and then thermoformed against a forming mandrel. This process produces a painted film preform that is subsequently placed within a molding press. The molding press injects a molten plastic material that adheres to the backing surface to produce the finished article.
It is desirable to produce finished articles that conform to the color and surface appearance of the adjacent article. This is especially true when the film-covered article is an automotive component such as a bumper fascia. The fascia is painted the same color as other body components and must display the same color, gloss and Distinction of Image (DOI) as the adjacent painted metal components. This usually requires painting the film with a colored layer and clear coat paints that match the paint of the adjacent metal components.
U.S. Pat. No. 4,913,760, teaches a method of placing the painted film on a temporary carrier and drying the painted film at successively higher temperature to avoid damaging the film. The temporary carrier is removed. The 4,913,760 reference does not teach heating the film prior to thermoforming to make it pliable nor heating the painted surface differently than the backing surface.
Heretofore, the film was placed within a heater or oven that evenly heated both surfaces of the film. The inventors found that heating both surfaces of the film often damaged the painted surface and reduced its appearance making it less suitable for use in automotive applications.
These deficiencies and problems are overcome by the present invention.